> For the complete documentation index, see [llms.txt](https://shapeshift.krud.dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://shapeshift.krud.dev/guides/instance-mapping.md).

# Instance Mapping

Due to the fact that ShapeShift uses reflection behind the scenes, destination **classes need a no arg constructor**. But in some cases you have no control over the destination classes and cannot modify them to add a no arg constructor. This is where Instance Mapping comes into play, you can pass already-instantiated destination objects to the `map` method.

{% hint style="info" %}
Version 0.0.7 of ShapeShift introduced new [Object Suppliers](/features/object-suppliers.md) functionality as an improved solution for the no arg constructor issue.
{% endhint %}

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
@DefaultMappingTarget(SimpleEntityDisplay::class)
data class SimpleEntity(
    @MappedField
    val name: String,
    @MappedField
    val description: String,
    val privateData: String
)
```

{% endtab %}

{% tab title="Java" %}

```java
@DefaultMappingTarget(SimpleEntityDisplay.class)
public class SimpleEntity {
    @MappedField
    private String name;
    @MappedField
    private String description;
    private String privateData;
    // Getters and Setters...
}
```

{% endtab %}
{% endtabs %}

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
data class SimpleEntityDisplay(
    val name: String,
    val description: String
)
```

{% endtab %}

{% tab title="Java" %}

```java
public class SimpleEntityDisplay {
    private String name;
    private String description;

    public SimpleEntityDisplay(String name, String description) {
        this.name = name;
        this.description = description;
    }
    // Getters and Setters...
}
```

{% endtab %}
{% endtabs %}

`SimpleEntityDisplay` does not have a no arg constructor. You can either add a no arg constructor or initiate a new instance of `SimpleEntityDisplay` and pass it to the `map` function.

{% tabs %}
{% tab title="Kotlin" %}

```kotlin
val shapeShift = ShapeShiftBuilder().build()
val simpleEntity = SimpleEntity("test", "test description", "private data")
val simpleEntityDisplay = SimpleEntityDisplay("", "")
// Passing simpleEntityDisplay as a destination instance 
val result = shapeShift.map(simpleEntity, simpleEntityDisplay)
```

{% endtab %}

{% tab title="Java" %}

```java
ShapeShift shapeShift = new ShapeShiftBuilder().build();
SimpleEntity simpleEntity = new SimpleEntity();
simpleEntity.setName("test");
simpleEntity.setDescription("test description");
simpleEntity.setPrivateData("private data");
SimpleEntityDisplay simpleEntityDisplay = new SimpleEntityDisplay("", "");
// Passing simpleEntityDisplay as a destination instance 
SimpleEntityDisplay result = shapeShift.map(simpleEntity, simpleEntityDisplay);
```

{% endtab %}
{% endtabs %}